git.sesse.net Git - vlc/blob - src/video_parser/vpar_synchro.c

   1 /*****************************************************************************
   2  * vpar_synchro.c : frame dropping routines
   3  *****************************************************************************
   4  * Copyright (C) 1999, 2000 VideoLAN
   5  * $Id: vpar_synchro.c,v 1.69 2001/01/10 19:22:11 massiot Exp $
   6  *
   7  * Authors: Christophe Massiot <massiot@via.ecp.fr>
   8  *          Samuel Hocevar <sam@via.ecp.fr>
   9  *          Jean-Marc Dressler <polux@via.ecp.fr>
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License as published by
  13  * the Free Software Foundation; either version 2 of the License, or
  14  * (at your option) any later version.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
  24  *****************************************************************************/
  25
  26 /*
  27  * DISCUSSION : How to Write an efficient Frame-Dropping Algorithm
  28  * ==========
  29  *
  30  * This implementation is based on mathematical and statistical
  31  * developments. Older implementations used an enslavement, considering
  32  * that if we're late when reading an I picture, we will decode one frame
  33  * less. It had a tendancy to derive, and wasn't responsive enough, which
  34  * would have caused trouble with the stream control stuff.
  35  *
  36  * 1. Structure of a picture stream
  37  *    =============================
  38  * Between 2 I's, we have for instance :
  39  *    I   B   P   B   P   B   P   B   P   B   P   B   I
  40  *    t0  t1  t2  t3  t4  t5  t6  t7  t8  t9  t10 t11 t12
  41  * Please bear in mind that B's and IP's will be inverted when displaying
  42  * (decoding order != presentation order). Thus, t1 < t0.
  43  *
  44  * FIXME: write a few words about stream structure changes.
  45  *
  46  * 2. Definitions
  47  *    ===========
  48  * t[0..12]     : Presentation timestamps of pictures 0..12.
  49  * t            : Current timestamp, at the moment of the decoding.
  50  * T            : Picture period, T = 1/frame_rate.
  51  * tau[I,P,B]   : Mean time to decode an [I,P,B] picture.
  52  * tauYUV       : Mean time to render a picture (given by the video_output).
  53  * tau´[I,P,B] = 2 * tau[I,P,B] + tauYUV
  54  *              : Mean time + typical difference (estimated to tau/2, that
  55  *                needs to be confirmed) + render time.
  56  * DELTA        : A given error margin.
  57  *
  58  * 3. General considerations
  59  *    ======================
  60  * We define three types of machines :
  61  *      14T > tauI : machines capable of decoding all I pictures
  62  *      2T > tauP  : machines capable of decoding all P pictures
  63  *      T > tauB   : machines capable of decoding all B pictures
  64  *
  65  * 4. Decoding of an I picture
  66  *    ========================
  67  * On fast machines, we decode all I's.
  68  * Otherwise :
  69  * We can decode an I picture if we simply have enough time to decode it
  70  * before displaying :
  71  *      t0 - t > tau´I + DELTA
  72  *
  73  * 5. Decoding of a P picture
  74  *    =======================
  75  * On fast machines, we decode all P's.
  76  * Otherwise :
  77  * First criterion : have time to decode it.
  78  *      t2 - t > tau´P + DELTA
  79  *
  80  * Second criterion : it shouldn't prevent us from displaying the forthcoming
  81  * I picture, which is more important.
  82  *      t12 - t > tau´P + tau´I + DELTA
  83  *
  84  * 6. Decoding of a B picture
  85  *    =======================
  86  * On fast machines, we decode all B's. Otherwise :
  87  *      t1 - t > tau´B + DELTA
  88  * Since the next displayed I or P is already decoded, we don't have to
  89  * worry about it.
  90  *
  91  * I hope you will have a pleasant flight and do not forget your life
  92  * jacket.
  93  *                                                  --Meuuh (2000-12-29)
  94  */
  95
  96 /*****************************************************************************
  97  * Preamble
  98  *****************************************************************************/
  99 #include "defs.h"
 100
 101 #include "config.h"
 102 #include "common.h"
 103 #include "threads.h"
 104 #include "mtime.h"
 105 #include "plugins.h"
 106
 107 #include "intf_msg.h"
 108
 109 #include "stream_control.h"
 110 #include "input_ext-dec.h"
 111
 112 #include "video.h"
 113 #include "video_output.h"
 114
 115 #include "../video_decoder/vdec_idct.h"
 116 #include "../video_decoder/video_decoder.h"
 117 #include "../video_decoder/vdec_motion.h"
 118
 119 #include "../video_decoder/vpar_blocks.h"
 120 #include "../video_decoder/vpar_headers.h"
 121 #include "../video_decoder/vpar_synchro.h"
 122 #include "../video_decoder/video_parser.h"
 123
 124 #include "main.h"
 125
 126 /*
 127  * Local prototypes
 128  */
 129 static int  SynchroType( void );
 130
 131 /* Error margins */
 132 #define DELTA                   (int)(0.040*CLOCK_FREQ)
 133 #define PTS_THRESHOLD           (int)(0.030*CLOCK_FREQ)
 134
 135 #define DEFAULT_NB_P            5
 136 #define DEFAULT_NB_B            1
 137
 138 /*****************************************************************************
 139  * vpar_SynchroInit : You know what ?
 140  *****************************************************************************/
 141 void vpar_SynchroInit( vpar_thread_t * p_vpar )
 142 {
 143     p_vpar->synchro.i_type = SynchroType();
 144     p_vpar->synchro.i_start = p_vpar->synchro.i_end = 0;
 145     vlc_mutex_init( &p_vpar->synchro.fifo_lock );
 146
 147     /* We use a fake stream pattern, which is often right. */
 148     p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p = DEFAULT_NB_P;
 149     p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b = DEFAULT_NB_B;
 150     memset( p_vpar->synchro.p_tau, 0, 4 * sizeof(mtime_t) );
 151     memset( p_vpar->synchro.pi_meaningful, 0, 4 * sizeof(unsigned int) );
 152     p_vpar->synchro.b_dropped_last = 0;
 153     p_vpar->synchro.current_pts = mdate() + DEFAULT_PTS_DELAY;
 154     p_vpar->synchro.backward_pts = 0;
 155     p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic =
 156         p_vpar->synchro.i_pic = 0;
 157 }
 158
 159 /*****************************************************************************
 160  * vpar_SynchroChoose : Decide whether we will decode a picture or not
 161  *****************************************************************************/
 162 boolean_t vpar_SynchroChoose( vpar_thread_t * p_vpar, int i_coding_type,
 163                               int i_structure )
 164 {
 165     /* For clarity reasons, we separated the special synchros code from the
 166      * mathematical synchro */
 167
 168     if( p_vpar->synchro.i_type != VPAR_SYNCHRO_DEFAULT )
 169     {
 170         switch( i_coding_type )
 171         {
 172         case I_CODING_TYPE:
 173             /* I, IP, IP+, IPB */
 174             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus )
 175             {
 176                 p_vpar->synchro.b_dropped_last = 1;
 177             }
 178             return( 1 );
 179
 180         case P_CODING_TYPE:
 181             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_I ) /* I */
 182             {
 183                 return( 0 );
 184             }
 185
 186             if( p_vpar->synchro.i_type == VPAR_SYNCHRO_Iplus ) /* I+ */
 187             {
 188                 if( p_vpar->synchro.b_dropped_last )
 189                 {
 190                     p_vpar->synchro.b_dropped_last = 0;
 191                     return( 1 );
 192                 }
 193                 else
 194                 {
 195                     return( 0 );
 196                 }
 197             }
 198
 199             return( 1 ); /* IP, IP+, IPB */
 200
 201         case B_CODING_TYPE:
 202             if( p_vpar->synchro.i_type <= VPAR_SYNCHRO_IP ) /* I, IP */
 203             {
 204                 return( 0 );
 205             }
 206             else if( p_vpar->synchro.i_type == VPAR_SYNCHRO_IPB ) /* IPB */
 207             {
 208                 return( 1 );
 209             }
 210
 211             p_vpar->synchro.b_dropped_last ^= 1; /* IP+ */
 212             return( !p_vpar->synchro.b_dropped_last );
 213         }
 214         return( 0 ); /* never reached but gcc yells at me */
 215     }
 216     else
 217     {
 218 #define TAU_PRIME( coding_type )    (p_vpar->synchro.p_tau[(coding_type)] \
 219                                  + (p_vpar->synchro.p_tau[(coding_type)] >> 1) \
 220                                             + tau_yuv)
 221 #define S                           p_vpar->synchro
 222         /* VPAR_SYNCHRO_DEFAULT */
 223         mtime_t         now, pts, period, tau_yuv;
 224         boolean_t       b_decode = 0;
 225 #ifdef DEBUG_VPAR
 226         char            p_date[MSTRTIME_MAX_SIZE];
 227 #endif
 228
 229         now = mdate();
 230         period = 1000000 / (p_vpar->sequence.i_frame_rate) * 1001;
 231
 232         vlc_mutex_lock( &p_vpar->p_vout->change_lock );
 233         tau_yuv = p_vpar->p_vout->render_time;
 234         vlc_mutex_unlock( &p_vpar->p_vout->change_lock );
 235
 236         vlc_mutex_lock( &p_vpar->synchro.fifo_lock );
 237
 238         switch( i_coding_type )
 239         {
 240         case I_CODING_TYPE:
 241             if( S.backward_pts )
 242             {
 243                 pts = S.backward_pts;
 244             }
 245             else
 246             {
 247                 /* displaying order : B B P B B I
 248                  *                      ^       ^
 249                  *                      |       +- current picture
 250                  *                      +- current PTS
 251                  */
 252                 pts = S.current_pts + period * (S.i_n_b + 2);
 253             }
 254
 255             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 256                     S.p_tau[I_CODING_TYPE] )
 257             {
 258                 b_decode = 1;
 259             }
 260             else
 261             {
 262                 b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
 263             }
 264             if( !b_decode )
 265                 intf_WarnMsg( 3, "vpar synchro warning: trashing I" );
 266             break;
 267
 268         case P_CODING_TYPE:
 269             if( S.backward_pts )
 270             {
 271                 pts = S.backward_pts;
 272             }
 273             else
 274             {
 275                 pts = S.current_pts + period * (S.i_n_b + 1);
 276             }
 277
 278             if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
 279                     S.p_tau[I_CODING_TYPE] )
 280             {
 281                 if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 282                 {
 283                     /* Security in case we're _really_ late */
 284                     b_decode = (pts - now > 0);
 285                 }
 286                 else
 287                 {
 288                     b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
 289                     /* next I */
 290                     b_decode &= (pts - now
 291                                   + period
 292                               * ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
 293                                 > (TAU_PRIME(P_CODING_TYPE)
 294                                     + TAU_PRIME(I_CODING_TYPE) + DELTA);
 295                 }
 296             }
 297             else
 298             {
 299                 b_decode = 0;
 300             }
 301             break;
 302
 303         case B_CODING_TYPE:
 304             pts = S.current_pts;
 305
 306             if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
 307             {
 308                 b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
 309             }
 310             else
 311             {
 312                 b_decode = 0;
 313             }
 314         }
 315
 316         vlc_mutex_unlock( &p_vpar->synchro.fifo_lock );
 317 #ifdef DEBUG_VPAR
 318         intf_DbgMsg("vpar synchro debug: %s picture scheduled for %s, %s (%lld)",
 319                     i_coding_type == B_CODING_TYPE ? "B" :
 320                     (i_coding_type == P_CODING_TYPE ? "P" : "I"),
 321                     mstrtime(p_date, pts), b_decode ? "decoding" : "trashed",
 322                     S.p_tau[i_coding_type]);
 323 #endif
 324 #ifdef STATS
 325         if( !b_decode )
 326         {
 327             S.i_not_chosen_pic++;
 328         }
 329 #endif
 330         return( b_decode );
 331 #undef S
 332 #undef TAU_PRIME
 333     }
 334 }
 335
 336 /*****************************************************************************
 337  * vpar_SynchroTrash : Update counters when we trash a picture
 338  *****************************************************************************/
 339 void vpar_SynchroTrash( vpar_thread_t * p_vpar, int i_coding_type,
 340                         int i_structure )
 341 {
 342 #ifdef STATS
 343     p_vpar->synchro.i_trashed_pic++;
 344 #endif
 345 }
 346
 347 /*****************************************************************************
 348  * vpar_SynchroDecode : Update timers when we decide to decode a picture
 349  *****************************************************************************/
 350 void vpar_SynchroDecode( vpar_thread_t * p_vpar, int i_coding_type,
 351                          int i_structure )
 352 {
 353     vlc_mutex_lock( &p_vpar->synchro.fifo_lock );
 354
 355     if( ((p_vpar->synchro.i_end + 1 - p_vpar->synchro.i_start)
 356             % MAX_DECODING_PIC) )
 357     {
 358         p_vpar->synchro.p_date_fifo[p_vpar->synchro.i_end] = mdate();
 359         p_vpar->synchro.pi_coding_types[p_vpar->synchro.i_end] = i_coding_type;
 360
 361         FIFO_INCREMENT( i_end );
 362     }
 363     else
 364     {
 365         /* FIFO full, panic() */
 366         intf_ErrMsg("vpar error: synchro fifo full, estimations will be biased");
 367     }
 368     vlc_mutex_unlock( &p_vpar->synchro.fifo_lock );
 369 }
 370
 371 /*****************************************************************************
 372  * vpar_SynchroEnd : Called when the image is totally decoded
 373  *****************************************************************************/
 374 void vpar_SynchroEnd( vpar_thread_t * p_vpar, int i_garbage )
 375 {
 376     mtime_t     tau;
 377     int         i_coding_type;
 378
 379     vlc_mutex_lock( &p_vpar->synchro.fifo_lock );
 380
 381     if (!i_garbage)
 382     {
 383         tau = mdate() - p_vpar->synchro.p_date_fifo[p_vpar->synchro.i_start];
 384         i_coding_type = p_vpar->synchro.pi_coding_types[p_vpar->synchro.i_start];
 385
 386         /* Mean with average tau, to ensure stability. */
 387         p_vpar->synchro.p_tau[i_coding_type] =
 388             (p_vpar->synchro.pi_meaningful[i_coding_type]
 389              * p_vpar->synchro.p_tau[i_coding_type] + tau)
 390             / (p_vpar->synchro.pi_meaningful[i_coding_type] + 1);
 391         if( p_vpar->synchro.pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
 392         {
 393             p_vpar->synchro.pi_meaningful[i_coding_type]++;
 394         }
 395 #ifdef DEBUG_VPAR
 396         intf_DbgMsg("vpar synchro debug: finished decoding %s (%lld)",
 397                     i_coding_type == B_CODING_TYPE ? "B" :
 398                     (i_coding_type == P_CODING_TYPE ? "P" : "I"), tau);
 399 #endif
 400     }
 401
 402     FIFO_INCREMENT( i_start );
 403
 404     vlc_mutex_unlock( &p_vpar->synchro.fifo_lock );
 405 }
 406
 407 /*****************************************************************************
 408  * vpar_SynchroDate : When an image has been decoded, ask for its date
 409  *****************************************************************************/
 410 mtime_t vpar_SynchroDate( vpar_thread_t * p_vpar )
 411 {
 412     /* No need to lock, since PTS are only used by the video parser. */
 413     return( p_vpar->synchro.current_pts );
 414 }
 415
 416 /*****************************************************************************
 417  * vpar_SynchroNewPicture: Update stream structure and PTS
 418  *****************************************************************************/
 419 void vpar_SynchroNewPicture( vpar_thread_t * p_vpar, int i_coding_type,
 420                              boolean_t b_repeat_field )
 421 {
 422     pes_packet_t *  p_pes;
 423     mtime_t         period = 1000000 / (p_vpar->sequence.i_frame_rate) * 1001;
 424
 425     switch( i_coding_type )
 426     {
 427     case I_CODING_TYPE:
 428         if( p_vpar->synchro.i_eta_p
 429                 && p_vpar->synchro.i_eta_p != p_vpar->synchro.i_n_p )
 430         {
 431             intf_WarnMsg( 1, "Stream periodicity changed from P[%d] to P[%d]",
 432                           p_vpar->synchro.i_n_p, p_vpar->synchro.i_eta_p );
 433             p_vpar->synchro.i_n_p = p_vpar->synchro.i_eta_p;
 434         }
 435         p_vpar->synchro.i_eta_p = p_vpar->synchro.i_eta_b = 0;
 436 #ifdef STATS
 437         if( p_vpar->synchro.i_type == VPAR_SYNCHRO_DEFAULT )
 438         {
 439             intf_Msg( "vpar synchro stats: I(%lld) P(%lld)[%d] B(%lld)[%d] YUV(%lld) : trashed %d:%d/%d",
 440                   p_vpar->synchro.p_tau[I_CODING_TYPE],
 441                   p_vpar->synchro.p_tau[P_CODING_TYPE],
 442                   p_vpar->synchro.i_n_p,
 443                   p_vpar->synchro.p_tau[B_CODING_TYPE],
 444                   p_vpar->synchro.i_n_b,
 445                   p_vpar->p_vout->render_time,
 446                   p_vpar->synchro.i_not_chosen_pic,
 447                   p_vpar->synchro.i_trashed_pic -
 448                   p_vpar->synchro.i_not_chosen_pic,
 449                   p_vpar->synchro.i_pic );
 450             p_vpar->synchro.i_trashed_pic = p_vpar->synchro.i_not_chosen_pic
 451                 = p_vpar->synchro.i_pic = 0;
 452         }
 453 #endif
 454         break;
 455     case P_CODING_TYPE:
 456         p_vpar->synchro.i_eta_p++;
 457         if( p_vpar->synchro.i_eta_b
 458                 && p_vpar->synchro.i_eta_b != p_vpar->synchro.i_n_b )
 459         {
 460             intf_WarnMsg( 1, "Stream periodicity changed from B[%d] to B[%d]",
 461                           p_vpar->synchro.i_n_b, p_vpar->synchro.i_eta_b );
 462             p_vpar->synchro.i_n_b = p_vpar->synchro.i_eta_b;
 463         }
 464         p_vpar->synchro.i_eta_b = 0;
 465         break;
 466     case B_CODING_TYPE:
 467         p_vpar->synchro.i_eta_b++;
 468         break;
 469     }
 470
 471     /* FIXME: use decoder_fifo callback */
 472     p_pes = DECODER_FIFO_START( *p_vpar->bit_stream.p_decoder_fifo );
 473
 474     if( b_repeat_field )
 475     {
 476         /* MPEG-2 repeat_first_field */
 477         /* FIXME : this is not exactly what we should do, repeat_first_field
 478          * only regards the next picture */
 479         p_vpar->synchro.current_pts += period + (period >> 1);
 480     }
 481     else
 482     {
 483         p_vpar->synchro.current_pts += period;
 484     }
 485
 486     if( i_coding_type == B_CODING_TYPE )
 487     {
 488         if( p_pes->i_pts )
 489         {
 490             if( p_pes->i_pts - p_vpar->synchro.current_pts > PTS_THRESHOLD
 491                  || p_vpar->synchro.current_pts - p_pes->i_pts > PTS_THRESHOLD )
 492             {
 493                 intf_WarnMsg( 2,
 494                         "vpar synchro warning: pts != current_date (%lld)",
 495                         p_vpar->synchro.current_pts - p_pes->i_pts );
 496             }
 497             p_vpar->synchro.current_pts = p_pes->i_pts;
 498             p_pes->i_pts = 0;
 499         }
 500     }
 501     else
 502     {
 503         if( p_vpar->synchro.backward_pts )
 504         {
 505             if( p_pes->i_dts &&
 506                 (p_pes->i_dts - p_vpar->synchro.backward_pts > PTS_THRESHOLD
 507               || p_vpar->synchro.backward_pts - p_pes->i_dts > PTS_THRESHOLD) )
 508             {
 509                 intf_WarnMsg( 2,
 510                         "vpar synchro warning: backward_pts != dts (%lld)",
 511                         p_vpar->synchro.backward_pts - p_pes->i_dts );
 512             }
 513
 514             if( p_vpar->synchro.backward_pts - p_vpar->synchro.current_pts
 515                     > PTS_THRESHOLD
 516                  || p_vpar->synchro.current_pts - p_vpar->synchro.backward_pts
 517                     > PTS_THRESHOLD )
 518             {
 519                 intf_WarnMsg( 2,
 520                    "vpar synchro warning: backward_pts != current_pts (%lld)",
 521                    p_vpar->synchro.current_pts - p_vpar->synchro.backward_pts );
 522             }
 523             p_vpar->synchro.current_pts = p_vpar->synchro.backward_pts;
 524             p_vpar->synchro.backward_pts = 0;
 525         }
 526         else if( p_pes->i_dts )
 527         {
 528             if( p_pes->i_dts - p_vpar->synchro.current_pts > PTS_THRESHOLD
 529                  || p_vpar->synchro.current_pts - p_pes->i_dts > PTS_THRESHOLD )
 530             {
 531                 intf_WarnMsg( 2,
 532                         "vpar synchro warning: dts != current_pts (%lld)",
 533                         p_vpar->synchro.current_pts - p_pes->i_dts );
 534             }
 535             /* By definition of a DTS. */
 536             p_vpar->synchro.current_pts = p_pes->i_dts;
 537             p_pes->i_dts = 0;
 538         }
 539
 540         if( p_pes->i_pts )
 541         {
 542 #if 0
 543             int     i_n_b;
 544 #endif
 545
 546             /* Store the PTS for the next time we have to date an I picture. */
 547             p_vpar->synchro.backward_pts = p_pes->i_pts;
 548             p_pes->i_pts = 0;
 549             /* FIXME : disabled because it conflicts with streams having
 550              * b_repeat_first_field */
 551 #if 0
 552             i_n_b = (p_vpar->synchro.backward_pts
 553                         - p_vpar->synchro.current_pts) / period - 1;
 554             if( i_n_b != p_vpar->synchro.i_n_b )
 555             {
 556                 intf_WarnMsg( 1,
 557                         "Anticipating a stream periodicity change from"
 558                         " B[%d] to B[%d]",
 559                               p_vpar->synchro.i_n_b, i_n_b );
 560                 p_vpar->synchro.i_n_b = i_n_b;
 561             }
 562 #endif
 563         }
 564     }
 565
 566 #ifdef STATS
 567     p_vpar->synchro.i_pic++;
 568 #endif
 569 }
 570
 571 /*****************************************************************************
 572  * SynchroType: Get the user's synchro type
 573  *****************************************************************************
 574  * This function is called at initialization.
 575  *****************************************************************************/
 576 static int SynchroType( void )
 577 {
 578     char * psz_synchro = main_GetPszVariable( VPAR_SYNCHRO_VAR, NULL );
 579
 580     if( psz_synchro == NULL )
 581     {
 582         return VPAR_SYNCHRO_DEFAULT;
 583     }
 584
 585     switch( *psz_synchro++ )
 586     {
 587       case 'i':
 588       case 'I':
 589         switch( *psz_synchro++ )
 590         {
 591           case '\0':
 592             return VPAR_SYNCHRO_I;
 593
 594           case '+':
 595             if( *psz_synchro ) return 0;
 596             return VPAR_SYNCHRO_Iplus;
 597
 598           case 'p':
 599           case 'P':
 600             switch( *psz_synchro++ )
 601             {
 602               case '\0':
 603                 return VPAR_SYNCHRO_IP;
 604
 605               case '+':
 606                 if( *psz_synchro ) return 0;
 607                 return VPAR_SYNCHRO_IPplus;
 608
 609               case 'b':
 610               case 'B':
 611                 if( *psz_synchro ) return 0;
 612                 return VPAR_SYNCHRO_IPB;
 613
 614               default:
 615                 return VPAR_SYNCHRO_DEFAULT;
 616
 617             }
 618
 619           default:
 620             return VPAR_SYNCHRO_DEFAULT;
 621         }
 622     }
 623
 624     return VPAR_SYNCHRO_DEFAULT;
 625 }
 626